Friction material composition, friction material using the same, and friction member

ABSTRACT

Provided is a friction material composition comprising: a binder; a fibrous base material; an abrasive material; an inorganic filler; and an organic filler,
         wherein the friction material composition further comprises:   at least one selected from the group consisting of zinc, a cellulose fiber as the fibrous base materials and a flame retardant fiber as the fibrous base materials;   an iron-based fiber as the fibrous base material in an specified amount; and   an inorganic abrasive material having a Mohs hardness of 8 or higher and a particle size of 1 μm or larger as the abrasive material in an amount of 1 wt % or less. The present invention can provide a friction material composition which is less destructive to facing materials compared to conventional products, which has a high friction coefficient upon braking when used in repeated braking during high-speed traveling, and which is capable of suppressing pad wear and uneven pad wear, in the case that the friction material composition is formed into a brake pad for passenger cars. The present invention can also provide a friction material and a friction member using this friction material composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of U.S. application Ser.No. 13/322,587, having a filing date of Nov. 28, 2011, which is aNational Stage of Entry of PCT/JP2009/063946, having an internationalfiling date of Aug. 6, 2009, which claims priority from Japanese patentapplication serial Nos. 2009-131993, filed Jun. 1, 2009, 2009-131996,filed Jun. 1, 2009, and 2009-131999, filed Jun. 1, 2009. The entirecontent of U.S. application Ser. No. 13/322,587 and PCT/JP2009/063946are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a friction material compositionappropriate for a friction material for a disc brake pad, brake liningand the like used in the braking of automobiles and the like, and afriction material using the friction material composition.

BACKGROUND ART

Friction materials such as disc brake pads, brake lining or the like areused for the purpose of braking of the automobiles and the like. Such afriction material plays the role of braking by being rubbed against anopposite material, for example, a disc rotor or a brake drum, forbraking. Therefore, the friction materials are not only required to havea high friction coefficient and stability in the friction coefficient,but also required to have characterristics that the friction materialdoes not easily shave a disc rotor which is a facing material (rotorwear), brake squeal does not easily occur (brake squealcharacteristics), and the pad service life is long (pad service life).

Furthermore, in recent years, friction materials are required to have aless decrease in the friction coefficient (fast fading characteristics),even under severe braking conditions such that the braking temperatureabnormally rises due to continuous high speed braking (a vehicle speedof 200 km/h or higher) or high deceleration braking (0.8 G or higher).

However, friction materials include a Low Steel material (hereinafter,also referred to as “LS material”) which contains steel fiber as afibrous base material and hard abrasive particles as an abrasivematerial, and a Non-Asbest Organic material (hereinafter, also referredto as “NAO material”) which does not contain steel fiber and containsalmost no hard abrasive particles.

The former has excellent fast fading characteristics but has inferiorrotor wear and inferior brake squeal characteristics. The latter hasexcellent rotor wear and excellent brake squeal characteristics, but hasinferior fast fading characteristics. Furthermore, NAO materials causelarge pad wear amounts during fast fading and frequently cause unevenwear of the pad as compared with the LS materials.

Heretofore, attempts have been made to improve in the fadingcharacteristics of NAO materials, and for example, it has been reportedto achieve an improvement by using a large amount of vulcanized rubberpowder instead of cashew dust and by increasing the thermal conductivity(see, for example, Patent Document 1), while it has been reported toachieve an improvement through the addition of activated alumina and afluoropolymer (see, for example, Patent Document 2). However, the effectof improving the fading characteristics in the high-speed range (avehicle speed of 200 km/h or higher) as described above, is notsufficient as compared with the characteristics of the LS materials.

PRIOR ART LITERATURES Patent Literatures

-   Patent Literature 1: Japanese Patent Application Laid-Open (JP-A)    No. 2007-254564-   Patent Literature 2: WO 2004/069954

DISCLOSURE OF THE INVENTION Technical Problem

As described above, there are many examples of making attempts toimprove the fast fading characteristics of NAO materials. However, thereis no instance of suggesting a friction material which achieves a goodbalance between the satisfactory fast fading characteristics in thehigh-speed range such as a vehicle speed of 200 km/h or higher, aspossessed by the LS materials, and the low rotor wear of the NAOmaterials, and currently there is a demand for a further improvedfriction material.

On the other hand, the fast fading characteristics and rotor wear of theLS materials are related to the amount of steel fiber and the amount ofhard abrasive particles. When the amounts of these materials are small,the fast fading characteristics are deteriorated, and when the amountsof these materials are large, rotor wear is deteriorated (increased).Accordingly, it is very difficult to making an improvement by achievinga balance between fast fading characteristics and rotor wear by usingthe composition of the LS materials.

In the present invention, it is an object to obtain a friction materialcomposition which achieves a good balance between the advantages of LSmaterials and the advantages of NAO materials, such that the frictionmaterial composition gives a friction material exhibiting a frictioncoefficient of a level equivalent to that of LS materials even under thefast fading conditions associated with an abnormal increased braketemperature due to repeated crash stops at a deceleration of 0.8 G froma vehicle speed of 200 km/h, and having a less pad wear amount anduneven wear during fast fading, and also exhibits less rotor wear.

Solution to Problem

In order to achieve the object described above, the inventors of thepresent invention conducted a thorough investigation on the relationshipamoung various combination of friction material-composition, fast fadingcharacteristics and rotor wear, and finally came to solve the problem.

Specifically, the inventors found that when at least any one of zinc, acellulose fiber as a fibrous base material and a flame retardant fiberas a fibrous base material, and an iron-based fiber as a fibrous basematerial are comprised in specific amounts into a friction materialcomposition, and the amount of a particular inorganic abrasive materialas an abrasive material is adjusted to a certain level or less, theremay be obtained a friction material composition which achieves a goodbalance between the advantages of LS materials and the advantages of NAOmaterials such that the friction material composition exhibiting afriction coefficient of a level equivalent to that of LS materials evenunder the fast fading conditions associated with an abnormal increasedbrake temperature due to repeated crash stops at a deceleration of 0.8 Gfrom a vehicle speed of 200 km/h, and having a less pad wear amount anduneven wear during fast fading, and also exhibiting less rotor wear; afriction material; and a friction member.

That is, the present invention relates to the following.

(1) A friction material composition comprising: a binder; a fibrous basematerial; an abrasive material; an inorganic filler; and an organicfiller,

wherein the friction material composition further comprises: zinc; aniron-base fiber as the fibrous base material in an amount of 2 to 10 wt%; and an inorganic abrasive material having a Mohs hardness of 8 orhigher and a particle diameter of 1 μm or larger as the abrasivematerial in an amount of 1 wt % or less.

(2) The friction material composition as set forth in the item (1),wherein the amount of the zinc is within the range of 2 to 5 wt %.

(3) The friction material composition as set forth in the item (1) or(2), comprising an aramid fiber as the fibrous base material in anamount of 1.5 wt % or more.

(4) The friction material composition as set forth in any one of theitems (1) to (3), comprising a flame retardant fiber as the fibrous basematerial.

(5) The friction material composition as set forth in the item (4),comprising the flame retardant fiber in an amount of 1 to 10 wt %.

(6) The friction material composition as set forth in any one of theitems (1) to (5), comprising a cellulose fiber as the fibrous basematerial.

(7) The friction material composition as set forth in the item (6),comprising the cellulose fiber in an amount of 1 to 10 wt %.

(8) The friction material composition as set forth in any one of theitems (1) to (7), comprising cashew dust as the organic filler in anamount of 1 to 10 wt %, wherein the cashew dust is coated with a liquidrubber in an amount of 3 to 17 wt % relative to the amount of the cashewdust.

(9) The friction material composition as set forth in any one of theitems (1) to (8), comprising activated alumina as the abrasive material,and comprising a fluoropolymer as the organic filler.

(10) The friction material composition as set forth in the item (9),wherein the activated alumina is an activated alumina having a specificsurface area calculated by a BET method of 150 m²/g or larger.

(11) The friction material composition as set forth in the item (9) or(10), wherein the activated alumina is γ-alumina.

(12) The friction material composition as set forth in any one of theitems (9) to (11), wherein the amount of the activated alumina is withinthe range of 1 to 10 wt % relative to the amount of the frictionmaterial composition.

(13) The friction material composition as set forth in any one of theitems (9) to (12), wherein the fluoropolymer is powder ofpolytetrafluoroethylene.

(14) The friction material composition as set forth in any one of theitems (9) to (13), wherein the amount of the fluoropolymer is within therange of 0.3 to 6 wt % relative to the amount of the friction materialcomposition.

(15) A friction material composition comprising: a binder; fibrous basematerials; an abrasive material; an inorganic filler; and an organicfiller;

wherein the friction material composition comprises: a cellulose fiberas the fibrous base materials; an iron-based fiber as the fibrous basematerials in an amount of 2 to 10 wt %; an inorganic abrasive materialhaving a Mohs hardness of 8 or higher and a particle diameter of 1 μm orlarger as the abrasive material in an amount of 1 wt % or less.

(16) The friction material composition as set forth in the item (15),comprising the cellulose fiber in an amount of 1 to 10 wt %.

(17) The friction material composition as set forth in the item (15) or(16), comprising an aramid fiber as the fibrous base material in anamount of 1.5 wt % or more.

(18) The friction material composition as set forth in any one of theitems (15) to (17), further comprising zinc.

(19) The friction material composition as set forth in the item (18),wherein the amount of the zinc is within the range of 2 to 5 wt %.

(20) The friction material composition as set forth in any one of theitems (15) to (19), comprising a flame retardant fiber as the fibrousbase material.

(21) The friction material composition as set forth in the item (20),comprising the flame retardant fiber in an amount of 1 to 10 wt %.

(22) The friction material composition as set forth in any one of theitems (15) to (21), comprising cashew dust as the organic filler in anamount of 1 to 10 wt %, wherein the cashew dust is coated with a liquidrubber in an amount of 3 to 17 wt % relative to the amount of the cashewdust.

(23) The friction material composition as set forth in any one of theitems (15) to (22), comprising activated alumina as the abrasivematerial, and comprising a fluoropolymer as the organic filler.

(24) The friction material composition as set forth in the item (23),wherein the activated alumina is an activated alumina having a specificsurface area calculated by a BET method of 150 m²/g or larger.

(25) The friction material composition as set forth in the items (23) or(24), wherein the activated alumina is γ-alumina.

(26) The friction material composition as set forth in any one of theitems (23) to (25), wherein the amount of the activated alumina iswithin the range of 1 to 10 wt % relative to the amount of the frictionmaterial composition.

(27) The friction material composition as set forth in any one of theitems (23) to (26), wherein the fluoropolymer is powder ofpolytetrafluoroethylene.

(28) The friction material composition as set forth in any one of theitems (23) to (27), wherein the amount of the fluoropolymer is withinthe range of 0.3 to 6 wt % relative to the amount of the frictionmaterial composition.

(29) A friction material composition comprising: a binder; fibrous basematerials; an abrasive material; an inorganic filler; and an organicfiller,

wherein the friction material composition comprises: a flame retardantfiber as the fibrous base materials; an iron-based fiber as the fibrousbase materials in an amount of 2 to 10 wt %, and an inorganic abrasivematerial having a Mohs hardness of 8 or higher and a particle diameterof 1 μm or larger as the abrasive material in an amount of 1 wt % orless.

(30) The friction material composition as set forth in the item (29),comprising the flame retardant fiber in an amount of 1 to 10 wt %.

(31) The friction material composition as set forth in the item (29) or(30), comprising an aramid fiber as the fibrous base material in anamount of 1.5 wt % or more.

(32) The friction material composition as set forth in any one of theitems (29) to (31), further comprising zinc.

(33) The friction material composition as set forth in the item (32),wherein the amount of the zinc is within the range of 2 to 5 wt %.

(34) The friction material composition as set forth in any one of theitems (29) to (33), comprising a cellulose fiber as the fibrous basematerial.

(35) The friction material composition as set forth in the item (34),comprising the cellulose fiber in an amount of 1 to 10 wt %.

(36) The friction material composition as set forth in any one of theitems (29) to (35), comprising cashew dust as the organic filler in anamount of 1 to 10 wt %, wherein the cashew dust is coated with a liquidrubber in an amount of 3 to 17 wt % relative to the amount of the cashewdust.

(37) The friction material composition as set forth in any one of theitems (29) to (36), comprising activated alumina as the abrasivematerial, and comprising a fluoropolymer as the organic filler.

(38) The friction material composition as set forth in the item (37),wherein the activated alumina is an activated alumina having a specificsurface area calculated by a BET method of 150 m²/g or larger.

(39) The friction material composition as set forth in the item (37) or(38), wherein the activated alumina is γ-alumina.

(40) The friction material composition as set forth in any one of theitems (37) to (39), wherein the amount of the activated alumina iswithin the range of 1 to 10 wt % relative to the amount of the frictionmaterial composition.

(41) The friction material composition as set forth in any one of theitems (37) to (40), wherein the fluoropolymer is powder ofpolytetrafluoroethylene.

(42) The friction material composition as set forth in any one of theitems (37) to (41), wherein the amount of the fluoropolymer is withinthe range of 0.3 to 6 wt % relative to the amount of the frictionmaterial composition.

(43) A friction material obtained by molding the friction materialcomposition as set forth in any one of the items (1) to (42).

(44) A friction member formed by integrating the friction materialobtained by molding the friction material composition as set forth inany one of the items (1) to (42), and a back metal.

Effect of the Invention

There can be provided a friction material composition which is lessdestructive to facing materials compared to conventional products, whichhas a high friction coefficient upon braking when used in repeatedbraking during high-speed traveling in the case that the frictionmaterial compositions is formed into a brake pad for passenger cars, andwhich is capable of suppressing pad wear and uneven pad wear; and afriction material and a friction member using this friction materialcomposition.

The disclosure of the present application is related to the subjectmatters described in Japanese Patent Application No. 2009-131993 filedon Jun. 1, 2009, Japanese patent Application No. 2009-131996 filed onJun. 1, 2009, and Japanese Patent Application No. 2009-131999 filed onJun. 1, 2009, the disclosures of which are incorporated herein byreference.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the friction material composition of the present invention,a friction material and a friction member using this friction materialcomposition will be described in detail.

The friction material composition of the present invention is a frictionmaterial composition comprising: a binder; a fibrous base material; anabrasive material; an inorganic filler; and an organic filler; and ischaracterized in that the friction material composition comprises atleast any one of zinc, a cellulose fiber as a fibrous base material anda flame retardant fiber as a fibrous base material, and 2 to 10 wt % ofan iron-based fiber as the fibrous base material, and the amount of aninorganic abrasive material having a Mohs hardness of 8 or higher and aparticle size of 1 μm or larger as the abrasive material is within therange of 1 wt % or more.

When the friction material composition has a constitution as describedabove, the amount of an abrasive material that is highly abrasive issmall and the amount of an iron-based fiber that causes adhesivefriction with the rotor surface is small. Therefore, the frictionmaterial composition exhibits less rotor wear, and fast fadingcharacteristics excellent in the combination of the zinc and a specificamount of the iron-based fiber, in the combination of the cellulosefiber and a specific amount of the iron-based fiber, and/or in thecombination of the flame retardant fiber and a specific amount of theiron-based fiber.

The “inorganic abrasive material having a Mohs hardness of 8 or higher”as used herein refers to an inorganic abrasive made of α-alumina,silicon carbide, boron carbide, titanium nitride, titanium carbide,boron carbide, silicon nitride or the like. Furthermore, the particlesize of such an abrasive is 1 μm or larger. The particle size is definedas D50 (medium diameter) obtained by a laser diffraction particle sizedistribution analysis.

The amount of the inorganic abrasive material having a Mohs hardness of8 or higher and a particle size of 1 μm or larger is preferably 1 wt %or less. When the amount is 1 wt % or less, adverse effects are noteasily exerted on the rotor wear and brake squeal characteristics.

The “iron-based fiber” as used herein refers to an iron-based alloyfiber such as a steel fiber or a stainless steel fiber, but from theviewpoint of rotor wear, a steel fiber is preferred. Furthermore, whenan iron-based alloy fiber such as a stainless steel fiber is used, it ispreferable that the total amount of the steel fiber and the iron-basedalloy fiber be within the range of 2 to 10 wt % and the amount of theiron-based alloy fiber be 1 wt % or less from the viewpoint of rotorwear. Furthermore, it is more preferable to comprise the iron-basedfiber in an amount of 2 to 8 wt % from the viewpoint of rotor wear.

When zinc is comprised, the friction coefficient during fast fading isimproved. The amount of addition of zinc is preferably within the rangeof 2 to 5 wt %. When the amount of addition of zinc is 2 wt % or more,it is easy to obtain fast fading characteristics. When the amount ofaddition is 5 wt % or less, pad wear can be prevented from increasing.Furthermore, there are no particular limitations on the shape of zinc,but it is preferable that the zinc be in a powder form.

It is preferable to comprise an aramid fiber as the fibrous basematerial in an amount of 1.5 wt % or more. When the amount of additionof the aramid fiber is 1.5 wt % or more, the effect of fast fadingcharacteristics can be easily obtained. Furthermore, it is preferablethat the aramid fiber has a fibrillar (ramified) shape.

When the friction material composition comprises a flame retardant fiberas the fibrous base material, the friction coefficient during fastfading is further enhanced. The flame retardant fiber as used herein isa precursor fiber of a PAN (polyacrylonitrile) carbon fiber, and is afiber obtainable by heat treating PAN fiber at the temperature withinthe range of 200° C. to 350° C. in the atmosphere.

The amount of addition of the flame retardant fiber is preferably withinthe range of 1 to 10 wt %. When the amount of addition of the flameretardant fiber is 1 wt % or more, an effect of improving the fastfading characteristics is obtained. When the amount of addition is 10 wt% or less, the friction coefficient at the ordinary use is not easilydecreased. The flame retardant fiber is such that, from the viewpoint ofdispersibility and the effect of reinforcement, the average fiber lengthis preferably within the range of 1 to 10 mm, and the average fiberdiameter is preferably within the range of 10 to 15 μm.

When a cellulose fiber is comprised as the fibrous base material, thefriction coefficient during fast fading is further enhanced. The amountof the cellulose fiber is preferably within the range of 1 to 10 wt %.When the amount of the cellulose fiber is 1 wt % or more, the effect ofimproving the fast fading characteristics can be easily obtained. Whenthe amount is 10 wt % or less, a decrease in the friction coefficientduring conventional use can be avoided.

As the binder comprised in the friction material composition for thepresent invention, a thermosetting resin that is conventionally used infriction materials can be used. Examples of the thermosetting resininclude a phenolic resin, and various modified phenolic resins such asan acryl-modified phenolic resin, a silicone-modified phenolic resin, acashew-modified phenolic resin, an epoxy-modified phenolic resin, and analkylbenzene-modified phenolic resin. Particularly, a phenolic resin, anacrylic-modified phenolic resin, and a silicone-modified phenolic resinare preferred, and these can be used singly or in combination of two ormore kinds.

Furthermore, the binder is preferably comprised in an amount of 5 to 20wt %, and more preferably comprised in an amount of 5 to 10 wt %, of thetotal amount of the composition. When the amount of the binder is inthis range, a decrease in the strength of the friction material can beavoided, and deterioration of the sound vibration performance such asbreak squeal due to increased elastic modulus, which is caused bydecreasing porosity of the friction material, can be avoided.

Examples of the other fibrous base materials (other than iron-basedfiber, aramid fiber, flame retardant fiber, and cellulose fiber) used inthe present invention include metal fibers, inorganic fibers, organicfibers, and carbon-based fibers.

As the metal fibers, copper fiber, brass fiber, bronze fiber, titaniumfiber, aluminum fiber and the like can be used as the metal fibers otherthan the iron-based fiber described above, and these fibers can be usedsingly or in combination of two or more kinds.

Examples of the inorganic fiber that can be used include ceramic fibers,biodegradable ceramic fibers, mineral fibers, glass fibers, potassiumtitanate fiber, silicate fibers, and wollastonite fiber, and these canbe used singly or in combination of two or more kinds. From theviewpoint of reducing environmental materials, it is preferable not tocomprise respirable potassium titanate fiber or respirable ceramicfibers.

As the organic fibers, acrylic fibers, phenolic resin fibers and thelike can be used as the organic fibers other than the aramid fiber andthe cellulose fiber described above, and these fibers can be used singlyor in combination of two or more kinds.

Examples of the carbon-based fibers that can be used include a PANcarbon fiber obtained by further carbonizing the flame retardant fiberdescribed above, a pitch carbon fiber, a PAN carbon fiber, and anactivated carbon fiber. These fibers can be used singly or incombination of two or more kinds.

All fibrous base materials such as the iron-based fiber and the aramidfiber are preferably comprised in an amount of 5 to 40 wt %, and morepreferably comprised in an amount of 10 to 30 wt %, relative to thetotal amount of the composition. When the amount is in this range, anoptimal porosity for friction materials can be obtained, and breaksqueal can be prevented. Also, an appropriate material strength can beobtained, and satisfactory moldability can be obtained.

In regard to the abrasive material used in the present invention,abrasive materials other than the abrasive material having a Mohshardness of 8 or higher as described above can be used. Examples of theabrasive materials other than the abrasive material having a Mohshardness of 8 or higher include zirconium silicate, zirconium oxide,mullite, chromite, titanium oxide, magnesium oxide, silica, iron oxide,and activated alumina such as γ-alumina, and these can be used singly orin combination of two or more kinds. Particularly, when γ-alumina isused, the fading phenomenon occurring at high temperature can besuppressed.

In regard to the specific surface area of the activated alumina, it isconsidered that the value calculated by a BET method is 150 m²/g ormore, preferably 180 m²/g or more, and more preferably within the rangeof 200 to 300 m²/g. When the specific surface area is 150 m²/g or more,there is a tendency that the effectiveness under such conditions as ahigh temperature is less decreased. The measurement of the specificsurface area can be carried out by, for example, a BET method based onnitrogen gas adsorption.

γ-alumina can be obtained by, for example, drying aluminum hydroxide ata low temperature to obtain alumina gel, and subjecting this alumina gelto calcination (activation treatment) at a temperature of 500° C. to800° C. Furthermore, commercially available products can also be used,and examples thereof include the activated alumina manufactured byMizusawa Industrial Chemicals, Ltd. (trade name: Neobead, specificsurface area: 230 m²/g).

Furthermore, the amount of the abrasive material (abrasive materialother than the abrasive material having a Mohs hardness of 8 or higher)is preferably within the range of 10 to 40 wt %, and more preferablywithin the range of 15 to 35 wt % relative to the amount of the frictionmaterial composition. When the amount is in this range, a braking effectis obtained, and the wear resistance and break squeal characteristicscan be ameliorated.

Furthermore, the content of γ-alumina is preferably within the range of1 to 10 wt % relative to the amount of the friction materialcomposition.

As the inorganic filler used in the present invention, for example,antimony trisulfide, tin sulfide, molybdenum disulfide, iron sulfide,bismuth sulfide, zinc sulfide, calcium hydroxide, calcium oxide, sodiumcarbonate, calcium carbonate, magnesium carbonate, barium sulfate,dolomite, cokes, graphite, mica, iron oxide, vermiculite, granularpotassium titanate, calcium sulfate, plate-like potassium titanate,talc, clay, and zeolite can be used, and these can be used singly or incombination of two or more kinds.

The amount of the inorganic filler is preferably within the range of 10to 40 wt %, and more preferably within the range of 15 to 35 wt %relative to the amount of the friction material composition. When theamount is in this range, deterioration of heat resistance can beavoided, and it is preferable also from the viewpoint of the balance inthe amounts of the other components of the friction material.

Examples of the organic filler comprised in the friction materialcomposition of the present invention include cashew dust, tire rubberpowder, acrylic rubber powder, isoprene rubber, NBR powder and SBRpowder, and these are used singly or in combination of two or morekinds. Furthermore, the amount of the organic filler is preferablywithin the range of 1 to 20 wt %, and more preferably within the rangeof 1 to 10 wt % relative to amount of the friction material composition.When the amount is in this range, an increase in the elastic modulus ofthe friction material and deterioration of the sound vibrationperformance such as break squeal can be avoided. Also, deterioration ofheat resistance and a decrease in the strength due to the thermalhistory can be avoided.

In the case of using cashew dust as the organic filler, it is preferableto coat the cashew dust with a liquid rubber in advance, because theoccurrence of segregation of cashew dust is suppressed. The amount ofthe liquid rubber is preferably within the range of 3 to 17 wt %relative to the amount of the cashew dust. When the amount of the liquidrubber is 3 wt % or more, the cashew dust does not easily drop out, andthe effect of adhesive force can be obtained. On the other hand, whenthe amount of the liquid rubber is 17 wt % or less, the frictionmaterial composition is not easily subjected to the adverse effects ofthe aggregation of cashew dust because of the adhesive force of theliquid rubber, and the cashew dust is easily dispersed, so that theoccurrence of segregation can be suppressed.

The amount of the coated cashew dust is preferably within the range of 1to 10 wt % relative to the amount of the friction material composition,from the viewpoint of preventing the occurrence of break squeal andpreventing the occurrence of cracks.

As the liquid rubber, it is preferable to use NBR, SBR, IR, acrylicrubber, natural rubber, chloroprene rubber and the like, and theviscosity of the liquid rubber is such that the melt viscosity at 20° C.is preferably within the range of 10,000 to 100,000 cps, more preferablywithin the range of 30,000 to 80,000 cps, and even more preferablywithin the range of 40,000 to 60,000 cps. When the viscosity is in therange described above, it is preferable because coating is sufficientlyachieved, and the cashew dust is not easily aggregated.

There are no particular limitations on the method of coating the cashewdust with a liquid rubber, but a method of kneading under pressure byusing a pressure kneader is preferred.

The friction material composition of the present invention can be usedas a friction material such as disc brake pads, brake lining and thelike for automobiles, or as a friction material for clutch facings,electromagnetic brakes, retaining brakes and the like, by subjecting thefriction material composition of the present invention to processes suchas molding, processing and bonding to obtain desired shapes.

Furthermore, in the friction material composition of the presentinvention, other materials can be incorporated as necessary, in additionto the materials described above, and for example, metal powders such ascopper powder, brass powder and bronze powder; or organic additives suchas fluoropolymers, for example PTFE (polytetrafluoroethylene), can beincorporated.

Particularly, when PTFE is used, the fading phenomenon at hightemperature can be suppressed. The amount of PTFE is preferably withinthe range of 0.3 to 6 wt %, more preferably within the range of 1 to 5wt %, and even more preferably within the range of 1 to 3 wt %, relativeto the amount of the friction material composition.

The fluoropolymers are preferably used in the form of powder, but evenif the fluoropolymers are used in the form of emulsion and areincorporated into the friction material composition by wet mixing,equivalent effects can be expected.

The friction material composition of the present invention can be usedper se as a friction material that constitutes a frictional surface, toobtain a friction member. Examples of the friction member using thefriction material composition include the following configurations.

(1) A configuration of a friction material only.

(2) A configuration having: a back metal; and a friction material formedon this back metal, the friction material being formed from the frictionmaterial composition of the present invention to constitute a frictionalsurface.

(3) A configuration of further including: a primer layer; and anadhesive layer between the back metal and the friction material in theconfiguration of the item (2), the primer layer intended for surfacemodification to increase the adhesive effect of the back metal, and theadhesive layer intended for adhesion of the back metal and the frictionmaterial.

Furthermore, the friction material of the present invention can beproduced by using a method that is generally used, and the frictionmaterial is produced by molding the friction material composition of thepresent invention, preferably by molding under heat and pressure. Moreparticularly, the friction material composition of the present inventionis uniformly mixed using a mixing machine such as a Lodige mixer, apressurizing kneader or an Eirich mixer, and this mixture ispreliminarily molded with a molding mold. The preliminary moldingproduct thus obtained is molded for 2 to 10 minutes under the conditionsof a molding temperature of 130° C. to 160° C., and a molding pressureof 20 to 50 MPa, and the molded product thus obtained is heat treatedfor 2 to 10 hours at 150° C. to 250° C.

Also, the molded product is subjected to painting, a scorch treatment,and a polishing treatment as necessary.

Since the friction material composition of the present invention has ahigh reinforcing effect, the friction material composition can also beused by molding the composition as an underlayer material for frictionmembers. The “underlayer material” is a layer which is interposedbetween a friction material constituting the frictional surfaces of afriction member and a back metal, and is intended for an enhancement ofshear strength between the friction material and the back metal.

EXAMPLES

The friction material composition of the present invention will bedescribed more specifically by way of Examples.

(Production of Disc Brake Pad)

Materials were mixed according to the mixing ratios indicated in Table 1to Table 5, and the friction material compositions of Examples 1 to 20and Comparative Examples 1 to 4 were obtained.

The method of coating cashew dust with IR rubber is as follows. First,100 parts by mass of cashew dust and 10 parts by mass of liquid IRrubber were subjected to pressure kneading for 3 minutes under apressure of 0.49 MPa, using a pressurizing kneader (manufactured byMoriyama Manufacturing Co., Ltd.).

This friction material composition was mixed with a Lodige mixer(manufactured by Matsubo Corp., trade name: Lodige Mixer M20), and thismixture was preliminarily molded with a molding press (manufactured byOji Kikai Kogyo Co., Ltd.). The preliminary molded product thus obtainedwas molded under heat and pressure for 5 minutes under the conditions ofa molding temperature of 145° C. and a molding pressure 30 MPa using amolding press (manufactured by Sanki Seiko Co., Ltd.), and the moldedproduct thus obtained was heat treated for 4.5 hours at 200° C.,polished using a rotary polishing machine, and subjected to a scorchingtreatment at 500° C. Thus, disc brake pads of Examples 1 to 20 andComparative Examples 1 to 4 were obtained.

In the Examples and Comparative Examples, disc brake pads each having afriction material projection area of 52 cm² were produced.

(Evaluation of Dropout of Cashew Dust)

Evaluation was carried out by placing the friction material compositionsof Examples 1 to 20 and Comparative Examples 1 to 4 obtained by themethod described above each separately in a bag made of polyethylene,swinging each of the friction material compositions 10 times, andmeasuring the mass of cashew dust that had dropped out in the bottom ofthe bag. The evaluation criteria are as follows.

A: The amount of dropout relative to the amount of incorporation ofcashew dust is 1 wt % or less.

B: The amount of dropout relative to the amount of incorporation ofcashew dust is 3 wt % or more.

(Evaluation of Heat Fading Characteristics)

An evaluation of the heat fading characteristics was carried out usingthe disc brake pads of Examples 1 to 20 and Comparative Examples 1 to 4produced by the method described above and using a brake dynamo tester.In this experiment, an evaluation of the inertia moment of Skyline V35manufactured by Nissan Motor Co., Ltd. was carried out using a Colettetype caliper of general pin-slide type and a ventilated disc rotor(FC190) manufactured by Kiriu Corp.

An effectiveness test was carried out according to SAE J2522, and thesmallest value among the friction coefficients occurring in the Fade-1Section during a set of 15 times in total of braking was evaluated.

(Evaluation of Fast Fading Characteristics)

An evaluation of fast fading characteristics was carried out using thedisc brake pads of Examples 1 to 20 and Comparative Examples 1 to 4produced by the method described above by using a brake dynamo tester.In this experiment, an evaluation of the inertia moment of Skyline V35manufactured by Nissan Motor Co., Ltd. was carried out using a Colettetype caliper of general pin-slide type and a ventilated disc rotor(FC190) manufactured by Kiriu Corp.

An examination according to JASO C427 (initial velocity 50 km/h, finalvelocity 0 km/h, deceleration 0.3 G, brake temperature prior to braking100° C., 200 times of braking) was carried out, and then a fast fadingtest (15 times of braking was carried out at an interval of 60 secondsunder the following conditions: initial velocity 200 km/h, finalvelocity 0 km/h, deceleration 0.8 G, brake temperature prior to 1^(st)braking 100° C.). Thus, the minimum value of friction coefficient in thefast fading test, the amount of pad wear, and the amount of uneven padwear in the sliding direction were measured.

(Evaluation of Rotor Wear)

A test portion having a size of 25 mm×25 mm×8 mm was cut out from thefriction material surface of each of the disc brake pads produced withthe friction compositions of Examples 1 to 20 and Comparative Examples 1to 4, and this test portion was pressed under a pressure of 73.5 kPaagainst a disc rotor rotating at a circumferential velocity equivalentto 130 km/h and was sustained in this state for 22 hours. Subsequently,the amount of rotor wear was measured. A ventilated disc rotor (FC190)manufactured by Kiriu Corp. was used as the disc rotor.

The results are presented in Tables 1 to 5.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Components Binder Phenolic resin (HP491UP 7 7 7 7 7 7 incorporatedmanufactured by Hitachi Chemical Co., Ltd.) Fibrous Aramid fiber (1F5382 2 2 2 2 2 base manufactured by Du Pont- material Toray Co., Ltd.)Copper fiber 15 15 15 15 15 15 Mineral fiber (RB240 1 1 1 1 1 —manufactured by LAPINUS FIRERS B.V.) Abrasive Zirconium oxide 27 27 2727 27 34 material γ-alumina manufactured by — — — — — — MizusawaIndustrial Chemicals, Ltd. α-alumina: Mohs hardness 8 to — — — — — — 9(A-31 manufactured by Showa Denko K.K.) Zircon sand — — — — — —Inorganic Potassium titanate 11 10 9 11 11 5 filler Barium sulfate(Barium sulfate 9 8 6 5 6 3 manufactured by Sakai Chemical Industry Co.,Ltd.) Mica 3 3 3 3 3 3 Graphite 3 3 3 3 3 3 Cokes 4 4 4 4 4 4 Tinsulfide 4 4 4 4 4 4 Calcium hydroxide 3 3 3 3 3 3 Vermiculite — — — — —— Molybdenum sulfide — — — — — — Organic Cashew dust (uncoated) 3 3 3 33 3 filler Cashew dust (coated) — — — — — — Steel fiber (#0 manufacturedby Global 5 5 5 5 5 5 Material Technologies, Inc.) Zinc (AN200manufactured by Toho Zinc 3 5 8 3 3 3 Co., Ltd.) Flame retardant fiber(Pyromex — — — 4 — 3 manufactured by Toho Tenax Co., Ltd.) Cellulosefiber (Neofiber manufactured by — — — — 3 3 Oji Seishi Co., Ltd.) PTFEpowder manufactured by Sumitomo — — — — — — 3M, Ltd. IR rubber coatingof cashew dust None None None None None None Dropout of cashew dust B BB B B B Heat fading Minimum value of friction coefficient 0.20 0.19 0.180.19 0.19 0.19 characteristics Fast fading Minimum value of frictioncoefficient 0.19 0.19 0.19 0.22 0.21 0.23 characteristics Amount of padwear (mm) 2.21 2.80 3.10 1.76 2.28 1.76 Amount of uneven pad wear insliding 0.31 0.35 0.50 0.30 0.59 0.17 direction (mm) Rotor wear (μm) 1.71.7 1.8 2.0 1.7 1.7

TABLE 2 Example 7 Example 8 Example 9 Example 10 Components BinderPhenolic resin (HP491UP 7 7 7 7 incorporated manufactured by HitachiChemical Co.. Ltd.) Fibrous Aramid fiber (1F538 2 2 2 2 basemanufactured by Du Pont- material Toray Co., Ltd.) Copper fiber 15 15 1515 Mineral fiber (RB240 1 1 1 1 manufactured by LAPINUS FIRERS B.V.)Abrasive Zirconium oxide 27 25 25 25 material γ-alumina manufactured by— 2 2 2 Mizusawa Industrial Chemicals, Ltd. α-alumina: Mohs hardness 8 —— — — to 9 (A-31 manufactured by Showa Denko K.K.) Zircon sand — — — —Inorganic Potassium titanate 11 11 10 9 filler Barium sulfate (Barium 98 7 5 sulfate manufactured by Sakai Chemical Industry Co., Ltd.) Mica 33 3 3 Graphite 3 3 3 3 Cokes 4 4 4 4 Tin sulfide 4 4 4 4 Calciumhydroxide 3 3 3 3 Vermiculite — — — — Molybdenum sulfide — — — — OrganicCashew dust (uncoated) — — — — filler Cashew dust (coated) 3 3 3 3 Steelfiber (#0 manufactured by Global 5 5 5 5 Material Technologies, Inc.)Zinc (AN200 manufactured by Toho Zinc 3 3 5 8 Co., Ltd.) Flame retardantfiber (Pyromex — — — — manufactured by Toho Tenax Co., Ltd.) Cellulosefiber (Neofiber manufactured by — — — — Oji Seishi Co., Ltd.) PTFEpowder manufactured by Sumitomo — 1 1 1 3M, Ltd. IR rubber coating ofcashew dust coated coated coated coated Dropout of cashew dust A A A AHeat fading Minimum value of friction coefficient 0.20 0.29 0.28 0.30characteristics Fast fading Minimum value of friction coefficient 0.190.19 0.19 0.20 characteristics Amount of pad wear (mm) 2.30 2.30 2.553.15 Amount of uneven pad wear in sliding 0.35 0.33 0.35 0.40 direction(mm) Rotor wear (μm) 1.7 1.8 1.9 1.8

TABLE 3 Example 11 Example 12 Example 13 Example 14 Example 15Components Binder Phenolic resin (HP491UP 7 7 7 7 7 incorporatedmanufactured by Hitachi Chemical Co., Ltd.) Fibrous Aramid fiber (1F5382 2 2 2 2 base manufactured by Du Pont- material Toray Co., Ltd.) Copperfiber 15 15 15 15 15 Mineral fiber (RB240 1 1 1 1 1 manufactured byLAPINUS FIRERS B.V.) Abrasive Zirconium oxide 27 27 27 25 25 materialγ-alumina manufactured by — — — 2 2 Mizusawa Industrial Chemicals, Ltd.α-alumina: Mohs hardness 8 to — — — — — 9 (A-31 manufactured by ShowaDenko K.K.) Zircon sand — — — — — Inorganic Potassium titanate 12 11 1212 11 filler Barium sulfate (Barium sulfate 7 6 7 6 5 manufactured bySakai Chemical Industry Co., Ltd.) Mica 3 3 3 3 3 Graphite 3 3 3 3 3Cokes 4 4 4 4 4 Tin sulfide 4 4 4 4 4 Calcium hydroxide 3 3 3 3 3Vermiculite — — — — — Molybdenum sulfide — — — — — Organic Cashew dust(uncoated) 3 3 — — — filler Cashew dust (coated) — — 3 3 3 Steel fiber(#0 manufactured by Global 5 5 5 5 5 Material Technologies, Inc.) Zinc(AN200 manufactured by Toho Zinc — 3 — — 3 Co., Ltd.) Flame retardantfiber (Pyromex — — — — — manufactured by Toho Tenax Co., Ltd.) Cellulosefiber (Neofiber manufactured by 4 3 4 4 3 Oji Seishi Co., Ltd.) PTFEpowder manufactured by Sunitomo — — — 1 1 3M, Ltd. IR rubber coating ofcashew dust None None Coated Coated Coated Dropout of cashew dust B B AA A Heat fading Minimum value of friction coefficient 0.20 0.20 0.200.30 0.29 characteristics Fast fading Minimum value of frictioncoefficient 0.20 0.21 0.20 0.20 0.21 characteristics Amount of pad wear(mm) 2.55 1.85 2.50 2.32 2.00 Amount of uneven pad wear in sliding 0.440.33 0.38 0.33 0.30 direction (mm) Rotor wear (μm) 2.0 2.0 1.9 1.8 1.9

TABLE 4 Example 16 Example 17 Example 18 Example 19 Example 20Components Binder Phenolic resin (HP491UP 7 7 7 7 7 incorporatedmanufactured by Hitachi Chemical Co., Ltd.) Fibrous Aramid fiber (1F5382 2 2 2 2 base manufactured by Du Pont- material Toray Co., Ltd.) Copperfiber 15 15 15 15 15 Mineral fiber (RB240 1 1 1 1 1 manufactured byLAPINUS FIRERS B.V.) Abrasive Zirconium oxide 27 27 27 25 25 materialγ-alumina manufactured by — — — 2 2 Mizusawa Industrial Chemicals, Ltd.α-alumina: Mohs hardness 8 to — — — — — 9 (A-31 manufactured by ShowaDenko K.K.) Zircon sand — — — — — Inorganic Potassium titanate 12 11 1212 11 filler Barium sulfate (Barium sulfate 7 6 7 6 5 manufactured bySakai Chemical Industry Co., Ltd.) Mica 3 3 3 3 3 Graphite 3 3 3 3 3Cokes 4 4 4 4 4 Tin sulfide 4 4 4 4 4 Calcium hydroxide 3 3 3 3 3Vermiculite — — — — — Molybdenum sulfide — — — — — Organic Cashew dust(uncoated) 3 3 — — — filler Cashew dust (coated) — — 3 3 3 Steel fiber(#0 manufactured by Global 5 5 5 5 5 Material Technologies, Inc.) Zinc(AN200 manufactured by Toho Zinc — — — — — Co., Ltd.) Flame retardantfiber (Pyromex 4 3 4 4 3 manufactured by Toho Tenax Co., Ltd.) Cellulosefiber (Neofiber manufactured by — 3 — — 3 Oji Seishi Co., Ltd.) PTFEpowder manufactured by Sunitomo — — — 1 1 3M, Ltd. IR rubber coating ofcashew dust None None Coated Coated Coated Dropout of cashew dust B B AA A Heat fading Minimum value of friction coefficient 0.21 0.20 0.220.30 0.30 characteristics Fast fading Minimum value of frictioncoefficient 0.20 0.21 0.20 0.19 0.20 characteristics Amount of pad wear(mm) 2.80 1.85 2.66 2.50 2.51 Amount of uneven pad wear in sliding 0.440.33 0.40 0.35 0.33 direction (mm) Rotor wear (μm) 2.0 2.0 1.8 1.8 1.8

TABLE 5 Comparative Comparative Comparative Comparative Example 1example 2 example 3 example 4 Components Binder Phenolic resin (HP491UP7 7 7 7 incorporated manufactured by Hitachi Chemical Co., Ltd.) FibrousAramid fiber (1F538 2 2 4 1 base manufactured by Du Pont- material TorayCo., Ltd.) Copper fiber 15 15 15 14 Mineral fiber (RB240 1 2 2 —manufactured by LAPINUS FIRERS B.V.) Abrasive Zirconium oxide 27 32 2410 material γ-alumina manufactured by — — — — Mizusawa IndustrialChemicals, Ltd. α-alumina: Mohs hardness 8 to — — — 4 9 (A-31manufactured by Showa Denko K.K.) Zircon sand — — — 10 InorganicPotassium titanate 12 12 15 — filler Barium sulfate (Barium sulfate 1111 11 — manufactured by Sakai Chemical Industry Co., Ltd.) Mica 3 4 3 —Graphite 3 4 3 2 Cokes 4 2 2 13 Tin sulfide 4 4 4 7 Calcium hydroxide 32 2 3 Vermiculite — — — 5 Molybdenum sulfide — — — 3 Organic Cashew dust(uncoated) 3 3 5 4 filler Cashew dust (coated) — — — — Steel fiber (#0manufactured by Global 5 — — 18 Material Technologies, Inc.) Zinc (AN200manufactured by Toho Zinc — — 3 1 Co., Ltd.) Flame retardant fiber(Pyromex — — — — manufactured by Toho Tenax Co., Ltd.) Cellulose fiber(Neofiber manufactured by — — — — Oji Seishi Co., Ltd.) PTFE powdermanufactured by Sunitomo — — — — 3M, Ltd. IR rubber coating of cashewdust None None None None Dropout of cashew dust B B B B Heat fadingMinimum value of friction coefficient 0.19 0.20 0.18 0.28characteristics Fast fading Minimum value of friction coefficient 0.140.11 0.09 0.21 characteristics Amount of pad wear (mm) 3.30 4.89 5.011.70 Amount of uneven pad wear in sliding 0.88 1.15 1.44 0.36 direction(mm) Rotor wear (μm) 1.8 2.2 2.6 35.5

Examples 1 to 20 exhibit fast fading characteristics equivalent to thesame characteristics of Comparative Example 4 which is an LS material,and it is clear that the rotor wear is remarkably small. Furthermore,even when compared with Comparative Examples 2 and 3 which areconventional NAO materials, Examples 1 to 20 exhibit markedly high fastfading characteristics, and it is clear that these Examples exhibitequivalent rotor wear.

When Examples 1 to 3 are compared with Comparative Example 1, it isclear that the combination of a small amount of an iron-based fiber andzinc has a conspicuous effect of improving the fast fadingcharacteristics.

When Example 11 is compared with Comparative Example 1, it is clear thatthe combination of a small amount of an iron-based fiber and a cellulosefiber has a conspicuous effect of improving the fast fadingcharacteristics.

When Example 16 is compared with Comparative Example 1, it is clear thatthe combination of a small amount of an iron-based fiber and a flameretardant fiber has a conspicuous effect of improving the fast fadingcharacteristics.

According to Examples 7 to 10, 13 to 15 and 18 to 20, it is clear thatwhen cashew dust is coated with a liquid rubber, an effect ofsuppressing the dropout of cashew dust is obtained.

According to Examples 8 to 10, 14, 15, 19 and 20, it is clear that thecombination of γ-alumina and a PTFE powder has an effect of improvingthe heat fading characteristics.

INDUSTRIAL APPLICABILITY

The friction material of the present invention that is exclusive forbrake pads for passenger cars has excellent effects such as describedbelow.

According to the present invention, there are provided a frictionmaterial composition which is less destructive to facing materials ascompared with conventional products, which has a high frictioncoefficient upon braking when a method such as used in repeated brakingduring high-speed traveling, and which is capable of suppressing padwear and uneven pad wear; and a friction material and a friction memberusing this friction material composition.

1. A friction material composition comprising: a binder; a fibrous basematerial; an abrasive material; an inorganic filler; and an organicfiller, wherein the fibrous base material includes a cellulose fiber andan iron-based fiber, the iron-based fiber included in the frictionmaterial composition in an amount of 2 to 10 wt %, and wherein theabrasive material includes an inorganic abrasive material having a Mohshardness of 8 or higher and a particle diameter of 1 μm or larger in anamount of 1 wt % or less.
 2. The friction material composition accordingto claim 1, comprising the cellulose fiber fiber in an amount of 1 to 10wt % relative to amount of the friction material composition.
 3. Thefriction material composition according to claim 1, wherein the fibrousbase material further includes an aramid fiber, the aramid fiberincluded in an amount of 1.5 wt % or more relative to amount of thefriction material composition.
 4. The friction material compositionaccording to claim 1, further comprising zinc.
 5. The friction materialcomposition according to claim 4, wherein the amount of the zinc iswithin the range of 2 to 5 wt %.
 6. The friction material compositionaccording to claim 1, wherein the fibrous base material further includesa flame retardant fiber.
 7. The friction material composition accordingto claim 6, comprising the flame retardant fiber in an amount of 1 to 10wt % relative to the amount of the friction material composition.
 8. Thefriction material composition according to claim 1, comprising cashewdust as the organic filler in an amount of 1 to 10 wt % relative to theamount of the friction material composition, wherein the cashew dust iscoated with a liquid rubber in an amount of 3 to 17 wt % relative to theamount of the cashew dust.
 9. The friction material compositionaccording to claim 1, wherein the abrasive material further includesactivated alumina as an abrasive material, and a fluoropolymer as theorganic filler.
 10. The friction material composition according to claim9, wherein the activated alumina is an activated alumina having aspecific surface area calculated by a BET method of 150 m²/g or larger.11. The friction material composition according to claim 9, wherein theactivated alumina is γ-alumina.
 12. The friction material compositionaccording to claim 9, wherein the amount of the activated alumina iswithin the range of 1 to 10 wt % relative to the amount of the frictionmaterial composition.
 13. The friction material composition according toclaim 9, wherein the fluoropolymer is a powder ofpolytetrafluoroethylene.
 14. The friction material composition accordingto claim 9, wherein the amount of the fluoropolymer is within the rangeof 0.3 to 6 wt % relative to the amount of the friction materialcomposition.
 15. A friction material obtained by molding the frictionmaterial composition according to claim
 1. 16. A friction member formedby integrating the friction material obtained by molding the frictionmaterial composition according to claim 15, and a back metal.